1. Field of the Invention
This invention relates to a method of producing cement clinker comprising preheating the raw cement powder in a suspension-type heat exchanger, de-acidifying in a fluidized bed, clinkering in a rotary kiln, andd subsequently cooling the clinker.
2. Discussion of Prior Art
In the production of cement clinker it is generally usual to remove mechanical and chemically bound water from raw cement powder, to de-acidify the raw cement powder to a certain degree in a suspension-type heat exchanger and to use a rotary kiln for the further de-acidification and the clinkering.
Because a major part of the de-acidification is effected in the rotary kiln in that practice, it has the disadvantage that particularly for high through pout rates the rotary kiln must have large dimensions, which are not desirable from the aspect of plant engineering.
For this reason numerous efforts have been made to deacidify the raw cement powder as far as possible before it enters the rotary kiln. For this purpose, e.g., fuel has been fed separately to the lowermost stage of the suspension-type heat exchanger in order to effect a further heating and de-acidification of raw material (German Patent Publication No. 23 24 656). But the effect of that practice is limited because the raw material is subjected to the elevated temperature only for a short time.
A further development in the production of cement clinker calls for de-acidifying the raw material as far as possible in a separate unit, which is connected between the suspension-type heat exchanger and the rotary kiln and may consist of a heated pneumatic conveyor for feeding the raw material from the suspension-type heat exchanger to a cyclone, which precedes the rotary kiln (French Pat. No. 2,197,827), or of a fluidized bed reactor, from which the raw material is charged into the rotary kiln through a smoke chamber and a cyclone (German Patent Publication No. 23 44 094). In both cases it is difficult to control the residence time which is required for an adequate de-acidification, particularly because the grading of the raw material usually varies. It is also difficult to discharge the coarse particles.
It is an object of the invention to provide a process in which the disadvantages of the known processes, particularly of those described hereinbefore are avoided, which permits a virtually complete de-acidification of the raw cement powder before it is charged to th, rotary kiln and which can be carried out with a reasonable structural expenditure.